1. Field of the Invention
The present invention relates to a fabrication process for an integrated circuit. More particularly, the present invention relates to a fabrication process for a polysilicon gate.
2. Description of the Related Art
In general, a gate is formed with polysilicon or other similar types of material. During gate definition, however, polysilicon tends to reflect the light used for the photolithography process and leads to photolithography errors. In the fabrication process of a semiconductor device, an anti-reflection layer is typically formed on the polysilicon layer before defining the gate to avoid the reflection of the light by the polysilicon layer. The anti-reflection layer is usually formed with a silicon oxynitride material and is removed after the gate is defined. Methods to remove the antireflection layer include etching with a hot phosphoric acid solution. The polysilicon, however, is easily corroded by the hot phosphoric acid, resulting in an incomplete gate structure or even a peeling of the gate.
FIGS. 1A to 1D are schematic, cross-sectional views showing the manufacturing of a gate structure according to the conventional practice.
Referring to FIG. 1A, a substrate 100 is provided, followed by a formation of a layer 101 on the substrate 100. Since the polysilicon easily reflects the photolithography light and results in photolithography errors in the subsequent definition of the polysilicon gate, a silicon oxynitride anti-reflection layer 103 is normally formed on the polysilicon layer 101 to prevent the reflection of light by the polysilicon layer 101 before defining the polysilicon gate. A photoresist pattern 106 is thereafter formed on the anti-reflection layer 103.
As shown in FIG. 1B, with the photoresist pattern 106 serving as a mask, the anti-reflection layer 103 (as shown in FIG. 1A) and the polysilicon layer 101 (as shown in FIG. 1A) are etched to form a polysilicon gate 102 on the substrate 100. The anti-reflection layer after the etching is designated by reference number 104.
Referring to FIG. 1C, the photoresist pattern 106 (as shown in FIG. 1B) is removed, exposing the anti-reflection layer 104.
Referring to FIG. 1D, the anti-reflection layer 104 above the polysilicon gate 102 is removed by a hot phosphoric acid solution to complete the formation of the polysilicon gate. The etching rate of the hot phosphoric acid to polysilicon is, however, relatively high, and the sidewall of the polysilicon gate is thereby easily corroded by the hot phosphoric acid, leading to a peeling of the gate.